The present invention relates generally to presses for the shaping and curing of pneumatic tires. More particularly, the present invention relates to mold height adjustment apparatus for tire curing presses. More specifically, the present invention relates to mold height adjustment apparatus which permits the quick and easy alteration of tire curing press components to accommodate tire molds of different sizes in the press so that a number of sizes of tires can be manufactured from time to time in the same tire curing press.
It has always been necessary to employ tire curing presses in a number of sizes to accommodate the large variety of pneumatic tire sizes required for vehicles of different sizes, weights and performance characteristics. Since tire shaping and curing operations are necessarily carried out at high pressures, it is required that tire curing presses be constructed of heavy steel members which can both manipulate the tire molds during press opening and closing and provide the requisite squeeze pressure to withstand the internal pressures encountered during the tire curing operation. Since the size and cost of tire curing presses varies greatly with tire size, it has long been economically advantageous to employ tire curing presses in a number of sizes as a function of tire size. Thus curing presses of different sizes are commonly manufactured for passenger tire, large passenger tire/small truck tire and truck tire applications or portions of tires falling in those categories.
Even within the above tire size categories there are numerous tire sizes which require molds of differing dimensions. While some mold dimensions for tire sizes within a particular category may be accommodated without altering the configuration of the press, it is widely recognized that tire curing presses within a category advantageously have a mold height adjustment capability to accommodate tire molds of different heights, so that a range of tire sizes can be optimally processed in a single tire curing press size.
Mold height adjustment apparatus operates to establish an adjusted position when the press is closed so that the upper and lower mold sections are separated a fairly short distance through which one of the mold sections is moved, normally by cylinders, to the fully closed position of the molds prior to the introduction of curing pressure within the closed mold sections. Various approaches have been taken over the years to effect mold height adjustment in tire curing presses to accommodate upper and lower mold sections having different combined heights when in the fully closed position. Generally, mold height adjustment mechanisms have employed spacers of different thickness or adjusting screw and nut arrangements to achieve the variable adjusted positioning of press components to optimize operating with mold sections of different heights.
In some instances cylindrical spacers of different thicknesses have been interposed between the cylinder rods and rod extensions which finally close the mold sections and apply the squeeze forces thereto. To achieve different adjusted positions a variety of different sized spacers is necessary for each of the squeeze cylinders, thus creating a significant inventory problem. While these spacers are not themselves expensive and do provide accurate mold height adjustment, they do add significant cost to the design of the presses and are time-consuming to change, which results in significant downtime and resultant loss of production for the presses. Due to the disassembly and handling requirements, mold change with some spacer installations may reach excessive downtime in that the time required may be several hours and approach eight hours in the instance of some large truck presses.
A variation of a spacer arrangement contemplates that the squeeze cylinder rods or rod extensions have a plurality of axially or vertically spaced annular grooves. A removable stop collar is selectively positioned in one of the grooves to engage a stop tube which surrounds the cylinder rods or rod extensions. This arrangement has essentially the same features and disadvantages as the conventional cylindrical spacers except that it is not necessary to inventory any significant number of stop collars, except as replacement or repair parts.
One type of adjusting screw and nut mold height adjustment apparatus which has long been used operates in conjunction with the positioning of the upper mold section of a tire mold. In this apparatus the crossbeam of the press is connected to the upper bolster supporting the top mold section by a single central adjusting sleeve which is externally threaded. An internally threaded ring engages the threads of the adjusting sleeve and is nonrotatably attached to the crossbeam. Therefore, rotation of the adjusting sleeve effects selective vertical positioning of the upper mold section relative to the lower mold section. A ring gear attached to the adjusting sleeve may be employed with other gearing to facilitate rotation of the adjusting sleeve.
Another type of adjusting screw and nut mold height adjustment apparatus operates in conjunction with the positioning of the lower mold section of a tire mold. In this apparatus the blind end of each of the squeeze cylinders is supported on an adjusting screw or stud which is externally threaded. An internally threaded nut engages the external threads on the adjusting screw and is journaled in the press frame. Each nut has an attached sprocket. A drive chain extending around the sprocket on each of the nuts for each squeeze cylinder permits simultaneous, equiangular rotation of each of the nuts to adjust the vertical position of each of the squeeze cylinders and thus the lower mold section.
The above-described adjusting screw and nut mold height adjustment mechanisms have the advantage that they are relatively easy to operate and set up in comparison with the above-described spacer arrangements. However, the clearance in the threads of the screw and nut seriously compromise the vertical location accuracy and concentricity positions of the mold part that is supported thereby, as compounded by wear. Additionally, the complexity and precision required to achieve even acceptable accuracy in these mechanisms add substantially to the cost of a curing press and constitute high-maintenance mechanisms.
Thus, the mold height adjustment mechanisms currently in use in the industry all possess a mixture of advantages and disadvantages and are somewhat designed to take into account the structure of the particular press. Therefore, no single type of mold height adjustment mechanism has achieved widespread acceptance in the industry.
Therefore, an object of the present invention is to provide mold height adjustment apparatus for a tire curing press which employs an indexing ring with discrete vertical steps of differing vertical heights which are selectively interposed between squeeze cylinder rods and a lower bolster of the press to provide mold height adjustment for a plurality of mold sizes. Another object of the invention is to provide such mold height adjustment apparatus wherein the indexing ring contains a plurality of discrete vertical steps for each squeeze cylinder, whereby rotation of the indexing ring simultaneously provides the desired mold height adjustment at each squeeze cylinder for a particular tire mold. A further object of the invention is to provide such mold height adjustment apparatus having a locking assembly which locks the indexing ring with a selected discrete vertical step aligned with the squeeze cylinder rod, while permitting release of the locking assembly for moving the indexing ring to another discrete vertical step, to be locked thereat for operating tire molds having a different height dimension.
Another object of the present invention is to provide mold height adjustment apparatus for a tire curing press which provides the positioning precision of prior art spacer mechanisms without the attendant disadvantages. Yet another object of the invention is to provide such mold height adjustment apparatus which is relatively easy to operate and set up in the manner of prior art adjusting screw and nut mechanisms without the attendant disadvantages. Still another object of the invention is to provide such mold height adjustment apparatus which permits effecting a mold height adjustment to accommodate a different mold size in a time interval of approximately 15 minutes rather than a matter of several hours.
Still another object of the present invention is to provide a mold height adjustment mechanism for a tire curing press wherein an indexing ring carries a plurality of attached spacers of differing sizes which are rotated in and out of alignment with the piston rods of the squeeze cylinder to thus make the spacers self-storing and thereby eliminate the need to inventory and store a large number of spacers at a location remote from the tire curing press. Another object of the present invention is to provide such mold height adjustment apparatus that requires a minimum of space within the body of the press such that an enlarged press envelope is not required to incorporate the operating components of the mold height adjustment apparatus. Another further object of the invention is to provide such mold height adjustment apparatus which is of relatively low cost, particularly as regards adjusting screw and nut mechanisms, which has minimal maintenance costs and downtime associated with prior art mold height adjustment mechanisms and which can be quickly and easily operated by a single individual operating a few noncomplex hydraulic controls and manual actuators.
In general, the present invention contemplates a tire curing press having a frame, a bolster for mounting a lower mold section, a cylinder mounted on the frame, a cylinder rod of the cylinder for moving the bolster and the lower mold section between a closed position and a partially open position, moveable indexing apparatus interposed between the cylinder rod and the bolster, and a plurality of steps of differing thickness on the indexing apparatus, whereby moving a selected one of the plurality of steps into alignment with the cylinder rod establishes a different partially open position of the lower mold section.